Method and apparatus for cleaning gas-swept heating surfaces



Jan. 5, 1954 B. o. BROMAN METHOD AND APPARATUS FOR CLEANING GAS-SWEPT HEATING SURFACES 3 Sheets-Sheet 1 Filed March 5, 1950 INVENTOR ATTORNEYQ Jan, 5, 1954 B. o. BROMAN METHOD AND APPARATUS FOR CLEANING GAS-SWEPT HEATING SURFACES 5 Sheets-Sheet 2 Filed March 5, 1950 INVENTOR Jan. 5, 1954 B. o. BROMAN 2,665,119

METHOD AND APPARATUS FOR CLEANING GAS-SWEPT HEATING SURFACES Filed March 5, 1950 5 Sheets-Sheet 5 j O, B1 0mazz/ Patented Jan. 5, 1954 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR CLEANING GAS-SWEPT HEATING SURFACES Bror 0. Broman, Stora Essingcn, Stockholm, Sweden The present invention relates to a method and an apparatus for cleaning heating surfaces swept by air or gas.

More particularly the invention relates to an improved method and apparatus for cleaning such heating surfaces during the operation thereof.

The invention specifically relates to such a method and apparatus embodying the circulation through the apparatus embodying the surfaces to be cleaned during the operation of the same of solid material with the solid material falling or cascading by gravity through the apparatus to be cleaned and impinging and ricocheting against the heating surfaces during the gravity drop to pick up by such impact material deposits from the heating surfaces.

The invention specifically has reference to such a method and apparatus in which steel pellets or shot are utilized as the cleaning particles.

The prior art indicates that a plurality of different methods have been utilized for cleaning gas swept heating surfaces. One instance applicable to the cleaning of steam boilers and economizers involves blowing down with steam or air. Additionally, it has been known in connection with cleaning of economizers and air preheaters in soda furnaces for cellulose plants to wash the surfaces with water or some alkaline solution.

Such methods of course embody great inconvenience and are possessed with certain inherent drawbacks and disadvantages.

For example, in connection with the apparatus utilized for blowing down operations the cost of the same is rather high and in carrying out such method considerable expense is attributable to the cost of the steam or compressed air utilized.

In washing heating surfaces with water or an alkaline solution, it is obvious that great stresses and strains are set up in an apparatus due to the strong temperature stresses arising when the hot heating surfaces are suddenly cooled which in many instances causes serious damage to the construction in a short period of time and in other instances produces the deleterious effect know as salt corrosion. Additionally an unfavorable influence is exerted upon the temperature conditions when washing with water since iiue gases, combustion air and feed water are subjected to heavy temperature drops when washing is effected.

Additionally, the aforementioned processes or methods are not continuous and must be performed at certain intervals. Cleaning of heating surfaces should be eifected at least once every eight hours, that is at least three times in every twenty-four hour period of continuous operation, which means that between the cleaning times the hue gas resistance increases considerably up to the time of the next cleaning. Obviously, such prior art methods necessitate manual control or operation with the attendant drawbacks.

It is further well known to utilize sand blasting or shot peening involving forcibly projecting and impinging with the aid of compressed air of solid articles against the surface to be cleaned. This method, however, has not proved satisfactory in use since it is obvious that heating surfaces are damaged and worn by shot or sand blasting.

In my prior application Serial No. 100,645, filed June 22, 1949, I have disclosed a method of cleaning gas swept heating surfaces in which solid cleaning particles are distributed Within the apparatus to be cleaned in a predetermined manner and the particles fall down upon and ricochet against the respective heating surfaces to be cleaned substantially through gravity force to obtain a very eiiective cleaning without any injurious effects on the apparatus to be cleaned. In carrying out that method I have further disclosed the circulation through the apparatus to be cleaned of the cleaning particles and conveying back to the feed inlet of the particles so that one and the same quantity of cleaning parhcles provides a continuous circuit through the apparatus to be cleaned. However, in my prior method there are disadvantages attendant in certain instances. For example, when cleaning the steam boilers of sulphate cellulose plants the cleaning particles will gradually receive a coating of sodium sulphate thereby reducing the cleaning effect. In other instances, moisture from the flue gases will be precipitated on to the cleaning particles if the temperature of the particles falls below the dew point of the fiue gases. This will result that the solid matter carried by the combustion gasessweepin the heating surfaces will more readily adhere to the cleaning particles which in turn will acquire rather thick deposits thereon with the tendency of the particles in their falling action to adhere to one another and to the particles of solid matter in the flue gases to form cakes which formation will hinder, in such cases, the continued circulation of the cleaning particles and tend to prevent proper uniform distribution thereof within the apparatus to be cleaned.

- Accordingly'the present invention has for a general object to provide a method and an apparatus for cleaning gas swept heating surfaces which is extremely economical, does not damage the heating surfaces or other parts of the apparatus being cleaned, utilizes solid cleaning particles, provides for efiective circulation of the same through the apparatus to be cleaned during the operation thereof and reconditions the cleaning particles while insuring their effectiveness for continued operation.

More particularly the invention relates to .a method and apparatus of the characterdescribed in which the cleaning particles are subjected to a cooling step after leaving the apparatus to be cleaned whereby the deposits of solid imatter adhering to the particles burst off andare readily separated.

The invention further has for an object the elimination of the major portion of the burst off deposits from the flow circuit. of the cleaning particles.

An additional object of the invention is to provide apparatus embodying means for uniformly distributing solid cleaning particles, preferably steel shot, into the apparatus to be cleaned so that the same can cascade therethrough by gravity action, impinge against and ricochet between the various heating surfaces to be cleaned to remove loose matter accompanying .the gases sweeping the surfaces and matter adhering to the surfaces by impact thereagainst,.a collecting means for the cleaning particles after they have passed through theapparatus, conveying means including fan and conduit means for recycling the particles to the inlet end and separating means for separating the particles from the matter adhering thereto before the cleaning particles are reintroduced into the distributor.

The invention has for additional objects to provide conduits for conveying aircontainingthe removed solid matter from the fan to the furnace chamber. A primary object is to provide an apparatus of the aforedescribed character including means for cooling and cleaning the particles after they have passed through the apparatus to be cleaned and means for separating burst off deposits of solid matter disassociated from the cleaning particles as a result of the cooling.

An additional object is to regulate the cooling step that the temperature of the cleaning particles is above the dew point of the flue gases in the apparatus to be cleaned.

Additional and more specific objects will be readily ascertained from the following detailed description and drawings giving by way of examples several forms of the invention and .in which:

Figure 1 is a diagrammatical view partly in section of one embodiment of the invention;

Figure 2 is a diagrammatic perspective view of another embodiment;

Figure 3 is a fragmentary vertical section of a part of the apparatus illustrated in Figure 2; and

Figures 4 and 5 illustrate respectively in vertical section and in plan a form of distributing member forthe particles.

As regards the drawing, Figure 1 discloses the invention with reference to heat interchanging apparatus that are associated with a boiler ,plant. The apparatus includes :two similar heating systerns each including a casing I embodying side walls and a top wall. An upperg-as inlet .1 communicates witheach casing through a side wall noted at 6. cyclone separator ,6, the lower outlet of which .2 for preheating primary combustion air, an

economizer 3 consisting of spaced banks of tubes extending through the casing in a horizontal relationship and a preheater 4 for secondary combustion air. are mounted vertically above one another. Above These respective tube means the casing is a collecting means generally de- This collecting means includes a communicates through bifurcated ducts 1 with thetwo casings I that are disclosed in the drawings. These ducts I each discharge into a fun nel-shaped member .8, the lower end of which isextended by a hollow-shaft [5 which is rotatably mounted and projects through the top wall of the casing and terminates above the tube means therein that constitute the preheater 4. A rotary distributing member indicated generally at 9 is secured to the bottom end of the hollow shaft and, as apparent from Figures 4 and 5, this rotary distributing member has an outer contour of spiral form that extends from the vicinity of the center rotation thereof outward toward and terminates at its greatest radius. An electric motor It and suitable gear means rotate the hollow shaft that supports the rotary distributing member 9 so that solidcleaningparticles, for instance shot pellets, are eifectively distributed within the casing above the tubesand spread throughout substantially the cross-sectional area of the casing so that they fall .by gravity and cascade through the .casing to impact and ricochet against the surfaces of the tubes to pick up material accumulated thereon and'to-dislodge material therefrom so as to-clean the tubes. The particles pass from the heating systems I down into pockets .!:i which are .provided with grids or screens for separating lumps or cakes of .solid .matter and from thence into a return pipe 12 leading to and communicating with the cyclone '6. In advance of the pockets II a fan J3 communicates with the pipe 2 to convey the particles thereby providing continuous circuit from the hopper 58 through the apparatus thence up through the cyclone and back to the apparatus. Thedistributing member as set forth hereinafter is so-sliaped that the cleaning particles are properly distributed throughout the cross sectional area of the apparatus to be cleaned since as the particles fall down through the distributor illustrated in Figure 4 they pass out radially of the pipe l5 and are hurled outwardly varying distances due to the shape of the distributing member, thus providing an eiiective distribution of the particles prior to the subsequent cascade action through the apparatus.

Communicating with the conduit 12 and as indicated .rearwardly of the connection between the pockets II and the conduit 12 is the outlet pipe of a fan I4 which is fed with flue gases or air from the preheater 2 for primary air efiecting warmer gas flow into conduit I? to prevent cooling of the cleaning particles to such a degree that the temperature thereof falls below the-dew point of the flue gases in the apparatus.

It is therefore clear that I have provided a processin which solidcleaning particles are distributed throughout the cross sectional area of an apparatus embodying gas swept heating. surfaces to be cleaned to establish a cascade or gravity fall of the particles through the apparatus whereby the cleaning particles impinge against and ricochet between heating surfaces to remove coatings therefrom and to pick up particles of solid matter accompanying the gases sweeping the surfaces since the gases are directed downwardly in the same direction as the direction of travel of the particles. The particles and the solid matter adhering thereto and accompanying the same are collected after they have passed the heating surfaces to be cleaned, into a circuit for cooling off the particles to burst off the deposits of solid matter adhering thereto while conveying the particles toward the inlet end of the apparatus to be cleaned where the burst off deposits are separated from the particles and the particles are reintroduced into the apparatus. The separated deposits together with the conveying air are removed from the separator, preferably of the cyclone type, and introduced into the combustion chamber.

The method further embodies the introduction of an additional air flow of hot air or flue gas for adjusting the temperature of the particles in the circuit before they are reintroduced into the apparatus. The air flow conveys the cleaning particles to the apparatus in such fashion that the cooling thereof before reintroducing the same into the apparatus is adjusted by preheating after cooling to such a degree that condensation of moisture from the flue gases in the apparatus on to the cleaning particles is prevented. When starting the heating plant after it has been idle, the particles are obviously cool and are then heated by the preheated air flow. This manner of operation eliminates to a great degree the risk of a subsequent baking or adhering together of the particles and the solid matter accompanying the gases in the heating system and removed from the heating surfaces to form the aforementioned cakes which formation would tend to interrupt the operations. This additional heat for the air flow is obtained, for example, by mixing preheated primary air for the operation of the heating system with atmospheric air in suitable proportions.

As set forth hereinafter the method further can embody the cleaning of the cleaning particles by passing the same through a bath of a suitable temperature before they are introduced into the conveying circuit or conduit. The method andapparatus hereinafter described further provides for separating loose solid matter carried by the flue gases from the cleaning particles before they enter the conveying circuit so that this loose solid matter accompanies the flue gases when the latter leave the flue gas outlet. As far as the method of operation is concerned for this step the same involves the throttling of the flue gas outlet to increase the velocity of the flue gases so that the same entrains therewith the loose solid material not adhering to cleaning particles and removes the same from the apparatus.

Figs. 2 and 3 illustrate anotherembodiment of the invention in which the numeral l denotes the apparatus to be cleaned, which is provided at its top with a cyclone 6 from which a rotating distributing member 9 is fed through a pipe l5. At the bottom the apparatus is provided with a receiving pocket ll connected with a separator I6 provided with a grid or screen for separating cakes and lumps of solid matter and furthermore the cleaning particles may also be washed in said pocket before they are caused to fall down through an injector l1 into the return pipe 12 which communicates with the cyclone 6. The deposits from the cleaning particles, which have been burst off by the flowing air, follow the air through a conduit l8 constituting the upper out.- let from the cycloneand which conduit is connected with a suction fan I9, preferably of the series type, so that the removed deposits are led off through a conduit ISa for further separation and utilization. The cleaning particles conveyed to the cyclone 6 through pipe [2 fall down through the cyclone and into the distributing means because of their greater weight and from there they fall or cascade through the apparatus again.

The loose solid matter dropping out of the apparatus together with the cleaning particles follows the flue gases and may be removed together with them and utilized by suitable means. In order that the solid matter shall not follow the particles to the pockets I I and burden the cyclone during the continued process, one condition is requisite however namely that the speed of the flue gases be so high that the particles are carried along by them. For this purpose, screens 20 (Fig. 3) are provided in the path of the flue gases in front of the flue gas outlet 2|, so that a throttling effect is obtained resulting in a greater velocity of flow of the flue gases to thereby draw ofi the loose solid matter.

Figs. 4 and 5 illustrate an embodiment of the distributing member '9. This member comprises two substantially cone-shaped plates 22 and 23, mounted above each other in vertically spaced relation and held together by means of preferably radial connections and stays. The upper plate 23 has an inlet 2 eccentrically secured to the pipe 15 provided for the feed of the cleaning particles from the cyclone 6. Preferably this eccentricity is adjustable, and because the outer contour of the plates is arranged along a helical line extending from the vicinity of the centre of rotation outwards towards their greatest radius, a desired distribution of the cleaning particles is obtainable. Beneath the inlet 24 there is provided a substantially conical wear resistant and guide member 25 of a wear-resistant material for absorbing the initial impact or attack of the cleaning particles, the substantially conical shape thereof preventing cleaning particles from remaining in the centre of the distributing member.

If the cooling of the cleaning particles after they have left the apparatus to be cleaned should happen to proceed too far, the cleaning particles may be preheated so as to obtain a temperature exceeding the dew point of the flue gases. A suitable device for this purpose is the fan l4 shown in Fig. 1, which is fed from any suitable source of hot air or hot gases, for instance as mentioned above, from the primary air preheater 2.

I claim:

1. A method of cleaning gas swept heating surfaces of heat interchanging apparatus during operation thereof and which apparatus are of the type embodying walls and inlet and outlet means for the gas and means providing heat exchange surfaces Within the walls including introducing shot pellets within the walls directly above the surfaces to be cleaned throughout substantially the cross-sectional area comprised between the walls so that the pellets fall by gravity and cascadelthrough theapparatus and impact andricochet against :the surfaces to :be cleaned :to :pick up materiaisaccumulated thereon and itoi dislodge particles :of material therefrom, collecting the pellets with the deposits adhering thereto :after they *havezpassed the heating surfaces, coolring the pellets to burst .off deposits of material adhering thereto, conveying the :pellets and burst off deposits to aseparating zone, separating the burst off deposits from -.the pellets in said :zone and reintroducing :the :cleaned pellets into the apparatus.

,2. Amethod of cleaning gas sweptiheating sur- ,faces of 'heat interchanging apparatus during operation thereof and which apparatus are :of the type embodying walls and iinletand outlet means dor the teas and means providing heat exchange surfaces within the walls including introducin shot pellets within the walls directly above the surfaces to the cleaned throughout substantially the crosswsectional area comprised between the walls so that the pellets fall by gravity and casscade through the apparatus and impact :and ;ricochet.against-the surfaces to be cleaned to pick ;up :material accumulated thereon :and :to dislodge material therefrom while directing .flue gases through the apparatus to flow downwardly in the same direction as the pellets to sweep :the surfaces :so that :the pellets remove particles of material accompany n the gases sweeping the surfaces, removing .free particles of material with the gas, collecting the pellets with the deposits adhering thereto after they have :passed the heating surfaces, cooling the pellets to burst :ofi deposits of material adhering thereto, convcying the pellets and burst 01f deposits to a separating izone, separating the :burst off deposits from the pellets in said zone :and reintroducing the cleaned pellets into the apparatus.

:3. ,A method as defined in and by claim '2 in whichthe direction and velocity of the gas is altered during removal to increase .the efficiency thereof in removing loose particles of material therewith.

s. ,A ,method :as defined in and by claim 1 in which the cooling step comprises intermingling a gaseous current with the pellets after they have :been collected.

:5, method as defined in and 'by claim 4 in which the gaseous current is a mixture of gas and zair.

'6. ,A method as defined in and by claim 1 and further including preheating the pellets to a temperature .in excess .of the dew point of the flue gases flowing through the apparatus after the cooling s p- A method as defined in and hy claim '1 in which the conveying and cooling steps are combined and comprise picking up the pellets with a confined air current which conveys the same to the separating zone.

,8. Amethod as defined in and by claim 7 in which :the burst off deposits of material from the pellets are removed from the separating zone and reintroduced into the apparatus to be cleaned for combustion therein.

9. Apparatus for cleaning gas swept heating surfaces of heat interchange apparatus of the ype embodying walls defining a casing, means providing heat exchange surfaces within the cas ing-and gas inlet and outlet means communicat ing with the casing comprising means disposed above the surface to be cleaned for continuously and simultaneously spreading shot pellets within the casing throughout substantially the crosssectional area thereof directly .above the surfaces 130 :belcleaned to provide for gravity fall through the apparatus .50 that the pellets cascade against the surfaces to :be cleaned .and impinge against material adhering thereto -to remove the same therefrom, collecting means for receiving the pellets after they have passed through the apparatus and have accumulated deposits of material thereon continuously operable cooling :means for cooling the pellets-to burst off-the deposits therefrom, separating rmeans for separating the pellets from the burst off deposits and at least one conduit for re-cycling the pellets through the apparatus.

'10. Apparatus as defined in and by claim 9 in which said conduit "is in communication with the collecting means and receives the pellets and the cooling means comprises at least one fan communicating with the conduit for continuously intermingling an air current with the pellets to burst off the deposits therefrom.

11. Apparatus as defined in and by claim 10 in which said conduit constitutes a return conduit between the col-lecting means and the separating means and said fan comprises a pressure fan for feedingcooling and'conveying air to said conduit and an additional fan in communication with said conduit for feeding additional conveying medium to provide desired temperature of the cooling and "conveying medium in the conduit.

12. Apparatus for cleaning gas swept heating surfaces of heat interchange apparatus including means for introducing solid cleaning particle into the apparatus above the surfaces to be cleaned to provide for gravity fall through the apparatus so that the particles cascade against the surfaces to be cleaned and impinge against material adhering thereto to remove the same therefrom, collecting means for receiving the cleaning particles after they have passed through the apparatus and have accumulated deposits of material thereon, cooling means for cooling the particles to burst off the deposits therefrom, separating means for separating the cleaning particles from the burst off deposits, at least one conduit for re-cycling the cleaning particles through the apparatus, in which the introducing means includes a rotatable distributing member embodying a substantially vertical shaft and having an outer contour extending from the vicinity of the center of rotation of the member in spiral outline toward-the greatest radius of the member.

13. Apparatus for cleaning gas swept heating surfaces of heat interchange apparatus including means for introducing .solid cleaning particles into the apparatus above the surfaces to be cleaned to provide for gravity fall through the apparatus so that the particles cascade against the surfaces 'to be cleaned and impinge against material adhering thereto to remove the same therefrom, collecting means .for receiving the cleaningparticles after they 'have passed through the apparatus and have accumulated deposits of material thereon, cooling means for cooling the particles 'toburst off the deposits therefrom, separating ,means for separating the cleaning particles from the burst .off deposits, at least one conduit for re-cycling the cleaning particles through the apparatus, ,in which the introducing means includes a rotatable hollow shaft and a rotatable distributing member adjustably eccentrically mounted onsaid shaft andsaid member having an outer contour of spiral form extending from the vicinity of the center of rotation thereof outward toward and terminating at its greatest radius to provide for effective distribution of the cleaning particles throughout the cross sectional area of the apparatus to be cleaned.

14. Apparatus as defined in and by claim 13 in which the distributing member includes a substantially conical shaped wear-resistant member the apex of which is directed upward to register with said hollow shaft to receive the initial impact of the cleaning particles and prevent the accumulation thereof adjacent the end of said hollow shaft.

15. Apparatus as defined in and by claim 9 and including a conveying conduit communicating with the separating means through which is removed deposits separated from the pellets.

16, Apparatus as defined in and by claim 15 and a suction fan communicating with said conveying conduit.

17. In heat interchanging apparatus, a casing including side walls and a top wall, an upper gas inlet communicating with the casing adjacent the top wall, tube means within the casing and through which fluid passes for heat exchanging relationship with gas flowing through the casing, a rotatable distributing member disposed within the apparatus above the tube means to be cleaned, said distributing member having a spiral outline in plan to effectively distribute solid cleaning particles throughout the cross sectional area of the casing, means for feeding solid cleaning particles to said distributing member so that after distribution within the casing the particles cascade by gravity through the casing and impinge against the tubes to be cleaned to remove material adhering thereto. said apparatus to be cleaned including a pocket at the lower end thereof for receiving cleaning particles and material removed from the heating surfaces, said pocket having an outlet, a conduit communicating with said outlet for receiving cleaning particles having deposits of material adhering thereto, a flue gas outlet for said apparatus disposed in advance of the outlet from said pocket, throttling means adjacent said flue gas outlet to increase the velocity of the flue gas flowing therethrough so that the same will entrain loose material removed from the surfaces to be cleaned and remove the same with the flue gases through the flue gas outlet, a cyclone separator including upper and lower outlets, said conduit communicating with said separator between the outlets, the means for feeding cleaning particles providing communication between the lower outlet of the cyclone and the distributing member and fan means communicating with said conduit for conveying said cleaning particles to said cyclone including a fan supplying cooling medium to cool the particles to burst off the deposits of material adhering thereto before the particles reach the cyclone.

18. Apparatus as defined in and by claim 1'7 in which the throttling means comprises a screen disposed in front of the flue gas outlet extending so as to change the direction and velocity of the flue gas flow to the outlet.

19. A method for cleaning gas-swept heating surfaces of heat interchange apparatus during operation thereof and which apparatus are of the type embodying walls and inlet and outlet means for the gas and means providing heat exchange surfaces within the walls includin introducing shot pellets within the walls directly above the surfaces to be cleaned throughout substantially the cross-sectional area comprised between the walls so that the pellets fall by gravity and casoade through the apparatus and impact and ricochet against the surfaces to be cleaned to pick up material accumulated thereon and to dislodge particles of material therefrom, collecting the pellets having material accumulated thereon and entraining the pellets in a closed current of cooling conveying medium to cool the pellets to burst 01f deposits therefrom, intro-= ducing the entrained pellets and burst oil deposits into a separating zone, removing the burst off deposits from said zone and reintroducing the cleaned pellets into the apparatus.

20. A method for cleaning gas-swept heating surfaces of heat interchanging apparatus during operation thereof and which apparatus are of the type embodying walls and inlet and outlet means for the gas and means providing heat exchange surfaces within the walls including continuously introducing and simultaneously spreading shot pellets directly within the walls directly above the surfaces to be cleaned throughout substantially a cross-sectional area comprised be-- tween the walls so that the pellets fall by gravity and cascade through the apparatus and impact and ricochet against the surfaces to be cleaned to pick up material accumulated thereon and to dislodge particles of material therefrom, continuously removing pellets with material accumulated thereon from the apparatus, and entraining the continuously moved pellets within a closed air stream having a temperature less than the temperature of the pellets to simultaneously burst off deposits from the pellets and convey the pellets and burst oft deposits away from said apparatus, introducing the pellets and burst ofi deposits into a separating zone, separating the deposits and reintroducing the pellets into the apparatus to be cleaned.

21. The method as defined in and by claim 20 including altering the direction of gas flow through the apparatus while simultaneously increasing the velocity thereof to entrain with the gas material dislodged from the surfaces to be cleaned prior to collecting the pellets.

BROR O. BROMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,795,348 Schmidt Mar. 10, 1931 1,916,337 Schmidt July 4, 1933 2,029,424 Hill Feb. 4, 1936 2,087,694 Malmros July 20, 1937 2,455,514 Mead Dec. 7, 1948 2,494,695 Fisher Jan. 17, 1950 2,499,358 Cooper et al. Mar. 7, 1950 FOREIGN PATENTS Number Country Date 243,498 Great Britain Dec. 3, 1925 587,774 Great Britain May 6, 1947 

